Casting mould of a piston

ABSTRACT

A casting mould may include a soluble and substantially ring-shaped casting core forming a cooling duct and having at least one support which bears the casting core during a casting process. The at least one support may have a pin with a needle-like point configured to penetrate the casting core and fix it onto the support.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent application DE-102011082935.0, filed on Sep. 19, 2011, the contents of which are hereby incorporated in its entirety.

TECHNICAL FIELD

The present invention relates to a casting mould of a piston of an internal combustion engine, having a soluble and substantially ring-shaped casting core according to the preamble of claim 1.

The invention also relates to a piston which is cast with such a casting mould.

BACKGROUND

DE 198 04 168 A1 discloses a generic casting mould of a piston of an internal combustion engine, having a soluble and substantially ring-shaped casting core for forming a cooling duct. This casting core is supported on two supports, what are known as sleeves, which form a subsequent inflow and outflow of the ring-shaped cooling duct in the connection region with the casting core. Each of the supports has a centre line which is inclined towards the outer circumference of the piston and an end which touches the soluble casting core and is arranged on the side of the outer circumference of the piston. In particular, a piston having increased strength should be created thereby.

GB 1 055 737 discloses a further casting mould for casting a piston, in which a soluble casting core is supported and held in position by means of four supports. The supports are connected fixedly to the soluble casting core.

To fasten in particular water-soluble casting cores to a casting mould for producing a piston of an internal combustion engine, blind or through holes are usually introduced into this casting core and then pins are inserted into these holes, which can be inserted on the other side into corresponding recesses on the casting mould. The pins are fastened to the casting mould. The casting core can thereby be held in position during casting of the piston. The introduction of the known holes and the assembly of the casting mould are however comparatively complex and therefore expensive.

SUMMARY

The present invention is therefore concerned with the problem of specifying for a casting mould of the generic type an improved or at least an alternative embodiment which in particular greatly simplifies the assembly of the same.

This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments form the subject matter of the dependent claims.

The present invention is based on the general concept of no longer providing a soluble and substantially ring-shaped casting core for forming a cooling duct in a casting mould of a piston with holes, in particular with blind holes, first, in which associated pins are inserted during assembly of the casting mould, as previously known, but instead providing the supports which bear this casting core with a needle-like point, which penetrates the casting core and fixes it on the support without the previous introduction of holes. To this end, the casting mould according to the invention has the soluble and substantially ring-shaped casting core for forming the cooling duct and at least one support which bears this casting core during the casting process. This support in turn has a pin with the above-mentioned point, which is so sharp that it penetrates the soluble casting core by simple pressing and fixes the latter on the support without holes which are complex and expensive to produce. The casting core is thus simply impaled on the needle-like point formed according to the invention, without further, in particular preparatory, work steps being necessary. The positioning and at the same time the fixing of the casting core on the casting mould can be greatly simplified by simply impaling the casting core on the needle-like point of the pins of the support. To position the casting core relative to the supports or relative to the casting mould, what are known as “Walder tongs” are used, as described in the invention of Siegfried Walder in his thesis “Development of a device for process-safe position of a salt core with a blind hole”. These “Walder tongs” are designed both for the positioning and fixing of conventional casting cores, that is, casting cores with a blind hole, and for positioning novel casting cores, that is, casting cores without a previously introduced blind hole. Of course, other systems, for example robot-supported systems can be used to position the casting core.

In an advantageous development of the solution according to the invention, retaining contours are formed on the point, which provide improved retention of the point in the casting core. Such retaining contours can for example be formed as prongs or as hooks, in particular as barbs, but also as undercut contours in the form of arrowheads, and ensure both easy penetration of the point into the casting core and reliable fixing of the point in the casting core. Such retaining contours can be produced simple and therefore also cost-effectively by machines.

The pin is expediently surrounded by the support which forms a sleeve and can for example form a subsequent inflow or outflow to the cooling duct. The pin bearing the point is thus guided and accommodated in the support and is therefore mounted in the latter in an exchangeable manner. The support itself keeps the subsequent inflow or outflow for the cooling duct free during the casting process, it of course being conceivable for the point of the pin to project only slightly beyond the support forming the sleeve. The diameter of the support thus defines the diameter of the subsequent inflow or outflow of the cooling duct.

In a further advantageous embodiment of the solution according to the invention, the pin and in particular the point of the same are formed from a hot-work tool steel or a hard metal. Hot-work tool steels are alloyed tool steels for uses in which the surface temperature of the subsequent tool during use can be up to several hundred ° C. Their high wear resistance is obtained by a hardening treatment and their heat-resistance is obtained by subsequent tempering, during which secondary carbides are deposited and residual austenite is converted into martensite during cooling. Hard metals however mean sintered carbide hard metals which are characterised by high hardness, high wear-resistance and in particular also hot hardness. For this reason they are used extensively in the equipment of tools such as casting moulds. Hard metals usually consist of approx. 90 to 94% tungsten carbide and 6 to 10% cobalt, the tungsten carbide grains being on average approx. 0.5 to 1 micrometre in size. The additionally provided cobalt fills the interspaces between the tungsten carbide grains. During sintering of the hard metals, high-melting hard materials in a finely comminuted state are mixed with an easily melting second material (additive bodies) and heated to temperatures below the melting point of the high-melting component (carbides), the temperature and the duration being selected so that the carbides agglomerate. Both hot-work tool steel and hard metal are particularly suitable for use in casting moulds for producing cast pistons.

Further important features and advantages of the invention can be found in the subclaims, the drawings and the associated description of the figures using the drawings.

It is self-evident that the features which are mentioned above and those which are still to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, with the same reference symbols referring to the same or similar or functionally identical components.

In the figures,

FIG. 1 schematically shows a possible embodiment of a casting mould according to the invention,

FIG. 2 schematically shows a detailed illustration of a needle-like point of a pin supporting a casting core,

FIG. 3 schematically shows a sectional illustration through the pin including the point.

DETAILED DESCRIPTION

According to FIG. 1, a casting mould 1 according to the invention of an otherwise not shown piston of an internal combustion engine has a soluble and substantially ring-shaped casting core 2 for forming a cooling duct in the subsequent piston. The casting core 2 is supported by means of at least two supports 3, 4, which are in the form of sleeves, during the actual casting process. In order to be able to fix the casting core 2 reliably on the supports 3, 4, these pins 5 (cf. also FIGS. 2 and 3) have a needle-like point 6, which penetrates the casting core 2 comparatively easily and thereby fixes it on the support 3, 4. The casting core 2 can for example be formed as a salt or sand core and be dissolved and washed out for example by water after the casting material has cooled.

To fix the casting core 2 better on the point 6 of the pin 5 and thus on the supports 3, 4, retaining contours 7 (cf. FIG. 2) can be formed on the point 6, which contours can in particular be formed as prongs or as hooks and in particular as barbs. The retaining contours 7 can of course also be formed simply as scales or undercuts.

If in particular FIG. 3 is considered, it can be seen that the pin 5 is surrounded by the support 3, 4 forming a sleeve, it being possible for said support 3, 4 to form for example a subsequent inflow or a subsequent outflow of the cooling duct formed by the casting core 2. The pin 5 and in particular the point 6 of the same can for example be formed from a hot-work tool steel or from a hard metal and thereby be comparatively resistant to temperature and wear. A length L of the point 6 can for example be approx. 5 to 6 mm, it being possible for the pin 5 to have a diameter D of approx. 2 mm. In general, not only can the point 6 have the geometries shown according to FIGS. 2 and 3, but also other, in particular leaf-shaped geometries are of course conceivable.

With the point 6 provided according to the invention at the end of the pins 5, the said casting core 2 can be fastened on the supports 3, 4 in a comparatively simple, fast and assembly-friendly manner, without further, in particular preparatory work, such as the production of blind holes in the casting core 2, being necessary. The point 6, which can in particular be needle-like, is so sharp that it penetrates the casting core 2 by light pressing against the same and thereby fixes the casting core 2 on the respective supports 3, 4. The casting mould 1 shown according to FIG. 1 should be understood merely by way of example, so of course casting moulds 1 having more or fewer supports 3, 4 are also included in the invention. The subsequently cast piston can for example be formed from aluminium, that is, as a lightweight metal piston.

The casting core 2 can furthermore be positioned and fixed on the supports 3, 4 comparatively easily by means of what are known as Walder tongs, these Walder tongs not being described in more detail, as they are described in detail in the thesis “Development of a device for process-safe position of a salt core with a blind hole” of Siegfried Walder. 

1. A casting mould, comprising: a soluble and substantially ring-shaped casting core for forming a cooling duct and having at least one support which bears the casting core during a casting process, wherein the at least one support has a pin with a needle-like point configured to penetrate the casting core and thereby fix it onto the support.
 2. The casting mould according to claim 1, wherein the casting mould is formed as at least one of a salt core and a sand core.
 3. The casting mould according to claim 1, further comprising retaining contours formed on the point to facilitate better retention of the point in the casting core.
 4. The casting mould according to claim 3, wherein the retaining contours are formed as at least one of prongs, hooks, and barbs.
 5. The casting mould according to claim 1, wherein the pin is surrounded by the support forming a sleeve, which forms at least one of a subsequent inflow and outflow to the cooling duct.
 6. The casting mould according to claim 1, wherein the pin and the point are formed from at least one of a hot-work tool steel and a hard metal.
 7. The casting mould according to claim 1, wherein the point has a length (L) of approximately 5-6 mm.
 8. The casting mould according to claim 1, wherein the point has a diameter (D) of approximately 2 mm.
 9. A cast piston for an internal combustion engine, comprising: an interior ring-shaped cooling duct for cooling the piston during operation of the internal combustion engine, wherein the cooling duct is produced by a casting mould.
 10. The cast piston according to claim 9, wherein the piston is formed from a lightweight metal alloy.
 11. The casting mould according to claim 2, further comprising retaining contours formed on the point to facilitate better retention of the point in the casting core.
 12. The casting mould according to claim 11, wherein the pin is surrounded by the support forming a sleeve, which forms at least one of a subsequent inflow and outflow to the cooling duct.
 13. The casting mould according to claim 12, wherein the pin and the point are formed from at least one of a hot-work tool steel and a hard metal.
 14. The casting mould according to claim 13, wherein the point has a length (L) of approximately 5-6 mm.
 15. The casting mould according to claim 14, wherein the point has a diameter (D) of approximately 2 mm.
 16. The casting mould according to claim 2, wherein the pin is surrounded by the support forming a sleeve, which forms at least one of a subsequent inflow and outflow to the cooling duct.
 17. The casting mould according to claim 2, wherein the pin and the point are formed from at least one of a hot-work tool steel and a hard metal.
 18. The casting mould according to claim 2, wherein the point has a length (L) of approximately 5-6 mm.
 19. The casting mould according to claim 2, wherein the point has a diameter (D) of approximately 2 mm.
 20. The casting mould according to claim 4, wherein the pin is surrounded by the support forming a sleeve, which forms at least one of a subsequent inflow and outflow to the cooling duct. 